STM32 DMA behaviour on copying from 8bit peripherial to 16bit memory

[kuldeepdhaka9]

Posted on July 10, 2014 at 16:32The original post was too long to process during our migration. Please click on the attachment to read the original post.

[waclawek.jan]

Posted on July 11, 2014 at 15:55

I don't use the 'F0 but reading RM0091 I'd say this is the expected behaviour of DMA in the 'F0, when MSIZE is different from PSIZE, regardless of PINC/MINC. In other words, this is the simplest possible DMA model - no FIFO and the transfers are 1:1 - padding the missing bits with 0 (or throwing away unneeded bits, depending on the ratio of sizes and transfer direction).

However, are you sure you can't access the packet memory as 8-bit? IMO the RM is not very clear in this respect. I personally would try MSIZE=PSIZE=8-bit first. If that fails, as plan B, you might perhaps try to transfer data from ADC to the ''regular'' RAM as 8-bit, and in a second step, using a timer-triggered memory-to-packet-memory 16-bit transfer... JW

[Tesla DeLorean]

Posted on July 11, 2014 at 16:42

Why couldn't you use 16-bit and halve the transfer size? Aren't the bytes just packed in contiguous memory cells?

[waclawek.jan]

Posted on July 11, 2014 at 17:09

> Why couldn't you use 16-bit and halve the transfer size? Aren't the bytes just packed in contiguous memory cells?

Well, the RM says something about the packet memory being 16-bit wide (RM0091 rev6, Table 113 on p.844, also on p.848 ''structured as 512 half-wordsby 16 bits''). However, further reading revealed the comment on p.872, ''The packet memory should be accessed only by byte (8-bit) or half-word (16-bit) accesses.'' Ergo, IMO, MSIZE=PSIZE=8-bit should work. JW

[kuldeepdhaka9]

Posted on July 11, 2014 at 18:55 The original post was too long to process during our migration. Please click on the provided URL to read the original post. https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I6ff&d=%2Fa%2F0X0000000bss%2FQ8tLUYP8LJbIa4463Nd2SpXN.Iz642HxvbyCJ2nZoS4&asPdf=false

[waclawek.jan]

Posted on July 11, 2014 at 19:13

Try to DMA into the ''normal'' RAM first.

JW

[kuldeepdhaka9]

Posted on July 13, 2014 at 06:18

Sorry for the delay. :)

PSIZE = 8, MSIZE = 8, ADC = 8bit, Channel1 = GND, Channel2 = VDDA using SRAM (not USB PMA) (gdb) x /100hx ain0_buffer 0x200001d0 <ain0_buffer>:    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00 0x200001e0 <ain0_buffer+16>:    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00 0x200001f0 <ain0_buffer+32>:    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00    0xff00 ............................. /**********************************************************************/ PSIZE = 8, MSIZE = 8, ADC = 8bit Channel1 = VDDA, Channel2 = GND using SRAM (not USB PMA) 0x200001d0 <ain0_buffer>:    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff 0x200001e0 <ain0_buffer+16>:    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff 0x200001f0 <ain0_buffer+32>:    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff    0x00ff ............................. /**********************************************************************/ PSIZE = 8, MSIZE = 16, ADC = 8bit Channel1 = GND, Channel2 = VDDA using SRAM (not USB PMA) 0x200001d0 <ain0_buffer>:    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff 0x200001e0 <ain0_buffer+16>:    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff 0x200001f0 <ain0_buffer+32>:    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff 0x20000200 <ain0_buffer+48>:    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff ............................. /**********************************************************************/ PSIZE = 8, MSIZE = 16, ADC = 8bit Channel1 = VDDA, Channel2 = GND using SRAM (not USB PMA) (gdb) x /100hx ain0_buffer 0x200001d0 <ain0_buffer>:    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000 0x200001e0 <ain0_buffer+16>:    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000 0x200001f0 <ain0_buffer+32>:    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000 0x20000200 <ain0_buffer+48>:    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000    0x00ff    0x0000 ............................. (gdb) x /100wx ain0_buffer 0x200001d0 <ain0_buffer>:    0x000000ff    0x000000ff    0x000000ff    0x000000ff 0x200001e0 <ain0_buffer+16>:    0x000000ff    0x000000ff    0x000000ff    0x000000ff 0x200001f0 <ain0_buffer+32>:    0x000000ff    0x000000ff    0x000000ff    0x000000ff 0x20000200 <ain0_buffer+48>:    0x000000ff    0x000000ff    0x000000ff    0x000000ff .............................